<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <form name="loginForm">
        <div>
            <label for="phoneInput">手机</label>
            <input type="text" name="phone" id="phoneInput" 
            placeholder="请输入手机" required 
            pattern="^[0-9]{11}$"/>
        </div>
        <div>
            <button type="submit">提交</button>
        </div>
    </form>
    <script>
        const oForm = document.forms["loginForm"];
        oForm.addEventListener('submit',function(event){
            event.preventDefault();
            const phone=oForm["phone"].value.trim();
            // console.log(typeof phone);
            // console.log(phone);
            // 判断字符串是否为空
            // require  html5 input才有的属性 对小白友好
            if(!phone.length){
                console.log('手机号不能为空');
                return;
            }
            if(!(/^[0-9]{11}$/.test(phone))){
                // console.log(phone.value);
                alert('手机格式有误');
                return;
            }
            this.submit();
        })
    </script>
</body>
</html>